*2.1. Computational Domain*

The pressure waves propagate in both forward and backward directions through the tube. If an exceedingly short tube was used in the numerical simulations, the pressure waves would reflect o ff the boundaries and cause unpredictable pressure variations [9,13]. Hence, a su fficiently long tube was chosen to fully analyze the pressure wave propagation. The simulation was conducted in a two-dimensional axisymmetric model. The nose and tail of the Hyperloop pod were assumed to have idealized semicircular geometries.

The BR is determined by the following equation:

$$BR = \frac{\text{Cross} - \text{sectional area of pool}}{\text{Cross} - \text{sectional area of tube}} = \frac{d\_{\text{pad}}^2}{d\_{\text{tube}}^2} \tag{1}$$

where *dpod* is the diameter of the pod and *dtube* is the diameter of the tube.

The pod's dimensions wereø3m × 43 m. The BR of 0.36 gave a tube diameter of 5 m and the BR of 0.25 gave a tube diameter of 6 m. The length of the tube was 1200 m. The computational geometry and boundary conditions used in the simulation are shown in Figure 1. Figure A1 (Appendix A) informs that the designed domain used in this simulation is long enough for the pressure wave to fully develop without losses (reflections).

**Figure 1.** Geometry and boundary conditions of the simulation. *dtube* = 5 m for BR = 0.36 and *dtube*= 6 m for BR = 0.25.
